MySQL questions

[Steve Holden]

"Billy Ng" <kwokng at earthlink.net> wrote ...
> Sorry guys, I can't get any help from the mysql newsgroup.  That's why I
> post it here.
>
Well, at least you tried ...

> Question 1
> I have a freq field that contains '"15:0" MINUTE_SECOND', why can't I do
> this?
>
> UPDATE table SET set next_update=DATE_ADD(NOW(), INTERVAL table.freq);
>
Perhaps if you explained what it was you were trying to do, then we might be
able to explain how to do it in SQL and/or Python. Seems like you want to
add an interval specified in hours and minutes (as a string?) in a row of
one table to a field in a row of some other table.

Is "freq" in the same table as "next_update"? Is there just one row in this
table?

If the table rows aren't huge, maybe you cxould even give us their
definition (from the "DESCRIBE table" SQL command).

> Question2
> How can I INSERT a record into the table if the table does not have any
> record with a provided id in the id field?  Do I need to join a SELECT
> statement?
>
You mean the table has no primary key? That would make it rather difficult
to uniquely specify (with a WHERE clause) which row to update. The usual way
to get around this is to use an INTEGER AUTO_INCREMENT field as the primary
key. When you insert into a table with such a key, but provide no value for
the key field (or specifically provide a NULL value) MySQL puts a unique
value for that field in the inserted row. You can retrieve the inserted
value in SQL using the last_inserted() or some similar function whose name
escapes me for the moment.

> Question3
> Can I query from a query in MySQL?
>
You mean can the output of one query become the input of another? Only if
you store the first query's output in a temporary table.

Most often, however, this isn't necessary if you make your SQL queries a
little more complex. Again, a few more details might help...

regards
 Steve
--

Steve Holden: http://www.holdenweb.com/ ; Python Web Programming:
http://pydish.holdenweb.com/pwp/